This invention is directed to a method of re-processing thermally stable polycrystalline diamond (“TSP”) materials to form new cutting elements and bits incorporating such cutting elements, as well as to such cutting elements and bits.
A TSP material is typically formed by “leaching” at least a substantial portion of a catalyst from polycrystalline diamond (“PCD”) using a leaching agent. When formed, polycrystalline diamond comprises individual diamond crystals that are interconnected defining a diamond network. A catalyst, which is used to facilitate the bonding of diamond crystals to form the PCD is often found within the interstitial spaces in the diamond network. Catalyst used in the formation of PCD include metals from the Group VIII of the Periodic Table, with cobalt being the most common. Cobalt has a significantly different coefficient of thermal expansion as compared to diamond, and as such, upon frictional heating of the polycrystalline diamond during use, the catalyst expands, causing cracking to form in the network structure, resulting in the deterioration of the polycrystalline diamond layer. Polycrystalline diamond having a second phase metal catalyst will generally not have thermal stability at temperatures above 700° C. By removing, i.e., by leaching, the catalyst (e.g., the cobalt) from the diamond network structure, the polycrystalline diamond layer becomes more heat resistant, as well as less prone to cracking when heated. Typically, strong acids are used to “leach” the catalyst from the diamond network structure.
Generally, to form a PCD layer, a substrate of cemented tungsten carbide (a substrate where tungsten carbide particles are cemented together with a binder such as cobalt) is placed adjacent to a layer of diamond particles, which may also be premixed with a catalyst, such as cobalt, in a refractory metal enclosure typically referred to as a “can”, as for example a niobium can, and the combination is subjected to a high temperature at a high pressure where diamond is thermodynamically stable. This process is referred to as a high-temperature-high-pressure sintering process (an “HTHP sintering process”). This process results in the recrystallization and formation of a polycrystalline diamond ultra hard material layer bonded on the tungsten carbide substrate. During the HTHP sintering process the catalyst helps form the bonds between the diamond particles forming the PCD. The PCD layer is then removed from the substrate by cutting off and by lapping off the substrate, as necessary. The removed PCD layer is then leached to substantially remove all of the catalyst to form the TSP material. Typically at least 95%, and in many cases over 99% of the catalyst is removed such that essentially a matrix of diamond bonded crystals, with no catalyst or mere traces of the catalyst, remain. In this regard the spaces occupied by the removed catalyst remain void. The TSP material layer may then be attached to another substrate by brazing, or by a high-temperature-high-pressure process (an “HTHP bonding process”) where a cemented tungsten carbide substrate is provided adjacent the TSP layer and is heated at a sufficient temperature and at a sufficient pressure to melt and get a binder, such as the cobalt in the tungsten carbide, to infiltrate the void spaces in the TSP material layer for attaching the TSP material to the substrate forming a TSP material cutting element, such as a TSP material cutter or compact. Moreover, an infiltrant such as a metal or metal alloy infiltrant, as for example copper, silver, copper alloys and silver alloys, which have a melting temperature that is lower than the melting temperature of the diamond particles, may also be used to infiltrate the TSP material when being attached to the substrate. Infiltrants bond the TSP material to the substrate by infiltrating the TSP material voids and are non-catalylizing. It should be noted that an HTHP bonding process is not a sintering process as is the HTHP sintering process referred in the formation on the PCD. Moreover, the times, temperatures and/or pressures in an HTHP bonding process may be different than those in an HTHP sintering process. For convenience the term “HTHP process” is used herein to refer to a process requiring high temperature and high pressure as for example an HTHP sintering process or on HTHP bonding process.
Currently, TSP material cutting elements and compacts are disregarded when a portion of their TSP layers wears by a pre-determined amount and/or the substrate on which they are attached on wears or erodes by a pre-determined amount. As TSP material layers are relatively expensive to manufacture, a way of re-processing and re-using such TSP material layers is desired.